1. Field of the Invention
The present invention relates to power actuated valves and in particular to a spring return actuator.
2. Description of the Prior Art
Our prior patent application, Power Actuated Valve, Ser. No. 708,698, filed July 26, 1976, now U.S. Pat. No. 4,046,350 describes power actuators as used with the spring return of the present invention. Power actuated valves lose operating power in cases of power failure or failure in the control mechanisms or connecting lines. In case of such failures it is desirable in some uses that the valve always fail open and in some other uses that the valve always fail closed. For these uses a spring return is commonly utilized with the power actuator. To insure adequate spring pressure through the entire stroke, these return springs are usually long and bulky. They require larger power actuators to offset the spring pressure on the forward stroke and they raise maintenance problems in tending to fly apart on disassembly. As used throughout this specification, "forward stroke" is defined as that operation of a valve actuator that compresses a coupled return spring.